1. Field of the Invention
The invention relates to an apparatus and method for diagnosing erectile disfunction, and more particularly, for diagnosing vasculogenic erectile disfunction by using Doppler frequency shift to measure penile blood velocity.
2. Description of Related Art
Male impotence is defined as the chronic inability to attain and/or maintain an erection of sufficient rigidity for sexual intercourse. This problem affects approximately 10 million American men, with increasing incidence in those of advanced age. Impotence is a source of great anxiety for many and is the subject of many thousands of visits to physicians and other medical professionals every year.
During a normal erection, neurochemical stimulation causes penile arterial inflow to increase in the paired cavernosal arteries. The result is increased blood flow into the corpora cavernosa. The subtunical venus plexus is compressed against the tunica albuginea, and venous outflow is reduced to trap blood in the corpora cavernosa. This combination of increased inflow and decreased outflow results in vascular congestion of the penis, tumescence, and rigidity sufficient for sexual intercourse. It is believed that abnormal reduction of blood flow to the cavernosal arteries and/or excess venal outflow, i.e. corporal venous leakage, are the primary physical causes of impotence. These abnormal blood flow characteristics to and from the cavernosal arteries can be caused by a number of factors, for example atherosclerotic vascular disease, traumatic arterial occlusive disease, or defective venoocclusive mechanisms.
By measuring blood velocity in the cavernosal arteries, duplex ultrasonography has been used successfully to diagnose inadequate arterial inflow and excessive outflow. Typically, a transducer emits ultrasound energy and a receiver receives ultrasound energy reflected from the blood. Electronic circuitry then measures frequency differences between the transmitted and received ultrasound energy, to calculate blood velocity. See, for example:
Bassiouny, et al., "Penile Duplex Sonography in the Diagnosis of Venogenic Impotence,"Journal of Vascular Surgery , Vol. 13, No. 1, pp. 75-83, Jan., 1991; PA1 Cochlin, D.L., et al., Urogenital Ultrasound, A Text Atlas, pp. 257-258; PA1 Kisslo, J., et al., ed., Basic Doppler Echocardiography , pp. 11-16 and 190; PA1 Levine, L.A., et al., "Measurement of Venogenic Impotence Penile Duplex Ultrasonography," Journal of Urology, 1990, 143:211A; PA1 Lue, T.F., et al., "Vasculogenic Impotence Evaluated by High-Resolution Ultrasonography and Pulsed Doppler Analysis," Radiology, 1985, 155:777-81; PA1 Lue, T.F., et al., "Functional Evaluation of Penile Arteries with Duplex Ultrasound in Vasodilator Induced Erection," Urol Clin North Am 1989, 16: 799-806; PA1 Meuleman, et al., "Assessment of Penile Blood Flow by Duplex Ultrasonography in 44 Men with Normal Erectile Potency in Different Phases of Erection," Journal of Urology, Vol. 147, pp. 51-56, Jan., 1992; and PA1 Quam, J.P., et al., "Duplex and Color Doppler Sonographic Evaluation of Venogenic Impotence," AJR, 1989; 159:1141-7. PA1 Advanced Technology Laboratories Ultramark 9 Ultrasound System brochure, 1993. PA1 Advanced Technology Laboratories C7-4 HDI Broadband Curved Array Scanhead brochure, 1993. PA1 Advanced Technology Laboratories Ultramark 9 Digital Computed Sonography System brochure. PA1 Medasonics Neuroguard Transcranial Doppler Noninvasive Blood Flow Monitoring System brochure. PA1 Medasonics F3PA Doppler Fetal Pulse Detector Ultrasound Stethoscope brochure.
See also U.S. Pat. No. 5,482,039 to Place. All of the above-listed documents are incorporated herein by reference.
The general calculations involved in determining blood velocity using Doppler shift are well known in the art. See, for example, U.S. Pat. No. 4,722,347to Abrams and Hovland, which is incorporated herein by reference. See also U.S. Pat. Nos. 4,334,543, 4,485,821, 5,205,292, and 5,284,146 , which are incorporated herein by reference. See also the following documents, which are attached to and form a part of the above-identified Provisional Application No. 60/023,959:
One of the key variables necessary for proper velocity calculations is the angle between the direction of transmitted/received ultrasound waves and the blood flow path. To achieve accurate velocity determinations, this angle, hereinafter called the angle of incidence or Doppler angle, must be known accurately and/or maintained with some precision.
With conventional ultrasound devices, selection and precise maintenance of this angle of incidence are difficult. Many ultrasound devices suitable for measuring penile blood flow are handheld. An important limitation of handheld devices is that the angle of incidence varies unacceptably from reading to reading over time, or even during a single reading. This variability is a result of the instability and imprecision inherent with handheld devices. The urologist does not know what the angle of incidence is, and even if a desired angle is known, achieving that desired angle reproducibly on repeat measurements is very difficult during a diagnostic procedure requiring many separate measurements. Even if the relevant calculations eliminate the need to know the precise angle, e.g. by taking velocity ratios so as to effectively eliminate the angle variable, the angle must be held constant. This instability represents a significant disadvantage with previous ultrasonography devices, a disadvantage that is heightened when taking measurements with respect to a readily movable organ such as the penis.
A further disadvantage of prior art ultrasonography devices, and particularly ultrasonography devices used for penile blood flow measurement, lies in the current uncertainty in the medical community concerning the proper timing of blood velocity measurements during a diagnostic procedure. Typically, the urologist or other medical professional takes an initial cavernosal artery flow velocity measurement. Then, papaverine or another suitable vasodilating agent is injected or transurethrally administered to induce erectile response. Further ultrasonographic examination follows, with a series of velocity measurements being taken over time after the vasodilator is introduced and after subsequent self-stimulation by the patient. Some urologists believe that if blood velocity increase is less than 25%, the patient is probably impotent; if greater than 75%, the patient is probably healthy. For increases between 25% and 75%, the urologist likely will perform additional tests.
More specifically, the urologist measures peak systolic and end diastolic velocities before injection and at 5, 10, and 30 minutes after application of the vasodilating agent. Normal peak systolic velocity is considered by some medical professionals to be about 25 cm/sec. A resistance index is calculated as the difference between the peak systolic and end diastolic velocities divided by the peak systolic velocity, or EQU R.I. =(Peak systolic velocity - End diastolic velocity) / Peak systolic velocity.
A resistance index approaching or equal to about 1 is considered to be indicative of a normal result.
Choosing the exact timing of the post-vasodilation measurements to achieve accurate diagnosis is the subject of the debate. For example, slower but otherwise normal erectile response often occurs in males of advanced age, so that premature ultrasonographic measurement might result in a false positive diagnosis. A need has arisen, therefore, to eliminate the uncertainties involved in examination timing.